a) Field of the Invention
The present invention relates to improvements of an accumulator for use in an air-conditioning or heat pump system, and more particularly to a suction accumulator suitable for use in an air-conditioning system of a motor vehicle.
b) Description of the Prior Art
Closed-loop refrigeration/heat pump systems conventionally employ a compressor that is meant to draw in gaseous refrigerant at relatively low pressure and discharge hot refrigerant at relatively high pressure. The hot refrigerant condenses into liquid as it is cooled in a condenser. A small orifice or valve divides the system into high and low-pressure sides. The liquid on the high-pressure side passes through the orifice or valve and turns into a gas in the evaporator as it picks up heat. At low heat loads it is not desirable or possible to evaporate all the liquid. However, liquid refrigerant entering the compressor (known as xe2x80x9cfloodingxe2x80x9d) causes system efficiency loss and can cause damage to the compressor. Hence it is standard practice to include an accumulator between the evaporator and the compressor to separate and store the excess liquid.
An accumulator for an automotive air-conditioner system is typically a metal can, welded together, and often has fittings attached for a switch and/or charge port. One or more inlet tubes and an outlet tube pierce the top, sides, or occasionally the bottom, or attach to fittings provided for that purpose. The refrigerant flowing into a typical accumulator will impinge upon a deflector or baffle intended to reduce the likelihood of liquid flowing out the exit.
Some prior art is concerned with reducing the turbulence of the inlet flow (U.S. Pat. No. 5,184,480) as a way to reduce liquid carryover. Other designs are more concerned with the coupling between the inner reservoir and the outlet passage (U.S. Pat. Nos. 5,660,058, 5,179,844, 4,627,247), mainly to reduce the pressure drop across the accumulator (a critical system performance parameter).
Another feature of the prior art is the inclusion of a desiccant in the accumulator. Some refrigerant systems are more susceptible to moisture ingression and damage than others, especially less modern systems. For many systems it is necessary to remove any moisture, and the accumulator is a convenient spot to house the desiccant. Many early designs featured desiccant cartridges and the like (U.S. Pat. Nos. 4,509,340, 4,633,679, 4,768,355, 4,331,001), but the typical modern usage is a fabric bag of some suitable shape, full of desiccant beads and secured to some inner feature of the accumulator (like the J-shaped outlet tube) where the beads will contact the liquid refrigerant.
A further feature typical of the prior art is the use of insulation placed around the outside of accumulators to modify the thermal characteristics (U.S. Pat. No. 5,701,795). This is an added expense and is only used when required to reduce flooding.
One common feature of accumulators in typical usage is that they employ some technique to return compressor oil to circulation. Compressor oil generally circulates with the refrigerant throughout the system, but tends to accumulate in the reservoir of the accumulator. A typical method to return oil to circulation involves utilizing an outlet tube for the refrigerant gas that dips low into the reservoir before exiting the accumulator. A small hole in the outlet tube at the low point will allow liquid to be entrained in the gas flow to the compressor. It is inevitable that some of this liquid will be refrigerant. This liquid refrigerant returning to the compressor reduces system efficiency.
In normal operation the gas returning to the compressor is quite cool compared to the liquid from the condenser. It is well known that the cooling capacity and efficiency of the refrigeration cycle can be increased if the returning gas is used to further cool the liquid before it reaches the expansion device (U.S. Pat. No. 5,075,967). In systems that use an accumulator with an oil pick-up hole the effect can be enhanced as the liquid refrigerant entrained by the oil pick-up hole is evaporated to cool the condensate. A heat exchanger that is used to transfer heat from the high-pressure side to the low-pressure side is referred to as a xe2x80x9csuction-line heat exchangerxe2x80x9d (SLHX) or an xe2x80x9cinternal heat exchangerxe2x80x9d (IHX). (xe2x80x9cInternalxe2x80x9d to the system, as compared to the condenser and evaporator that exchange heat between the system and the environment.) The typical heat exchanger in HVAC application is fin and plate. The prior art recognizes that a conventional heat exchanger can be used as an IHX (U.S. Pat. No. 5,562,157, U.S. Pat. No. 5,609,036, U.S. Pat. No. 5,687,419), but generally mobile applications do not have room for a larger evaporator and cannot economically justify another component. Combining the IHX with the accumulator can provide a cost-effective solution that requires only incrementally more space and weight.
Several examples of prior art suggest that a coil or section of tube containing hot condensate can be located within the reservoir section of the accumulator for heat exchange (U.S. Pat. No. 5,075,967, U.S. Pat. No. 5,245,833, U.S. Pat. No. 5,622,055), however such designs are not optimal. The hot condensate will boil the low-pressure liquid in the accumulator reservoir, defeating the purpose of the reservoir and reducing system efficiency by loading the system with gas. There is a requirement for an internal heat exchanger combined with an accumulator in a simple, cost and space effective configuration that is easily manufactured and preserves the accumulator function.
In our International PCT Application No. PCT/CA01/00083 filed Jan. 25th, 2001 we have disclosed a suction accumulator of advanced design which includes a number of important improvements rendering it particularly suitable for use in vehicle air-conditioning systems. The disclosure of the aforesaid International PCT application is incorporated herein in its entirety.
The present invention provides a still further improved suction accumulator.
More specifically, the invention provides an accumulator for use in an air-conditioning or heat pump system comprising: a hermetically sealed outer housing comprising a top, an inlet opening, an outlet opening, a peripheral side wall, and a base; an inner liner positioned within said outer housing, said inner liner having a peripheral wall and a base which form a container to receive refrigerant delivered through said inlet opening, said inner liner being spaced from the peripheral wall and the base of said outer housing to define therewith an annular passage; a heat exchange tube positioned in said annular passage, said tube designed and configured to effect transfer of heat within said system from high pressure refrigerant to low pressure refrigerant, said tube having inlet and outlet ends that extend exteriorly of said outer housing; transfer passages at respective upper and lower ends of said annular passage, one-said transfer passage comprising an inlet communicating said annular passage to the interior of the inner liner and the other said transfer passage comprising an outlet communicating said annular passage to the exterior of said housing via said outlet opening; the arrangement being such that vaporized refrigerant drawn from said inner liner enters said annular passage through said one transfer passage, flows through said annular passage and along said heat exchange tube to said other transfer passage from where it exits said accumulator via said outlet opening. The flow of refrigerant gas in said annular passage can be in either direction as preferred.
The invention also provides an accumulator for use in an air-conditioning system comprising: a hermetically sealed outer housing comprising a cap, an inlet opening, an outlet opening, a peripheral side wall, and a base; an inner liner positioned within said outer housing, said inner liner having a peripheral wall and a base which form a container to receive refrigerant delivered through said inlet opening, said inner liner being spaced from the peripheral wall and the base of said outer housing to define therewith an annular clearance, said inner liner having an upper end that lies in contact with or adjacent said cap; a transfer passage for delivering refrigerant vapour from said container to said outlet opening; an internal heat exchanger for the high-pressure refrigerant being positioned in said annular clearance, said heat exchanger having inlet and outlet ends that extend exteriorly of said outer housing; wherein said inner liner is of low thermal conductivity to shield liquid refrigerant from excessive heat transfer from said outer container or from said coil.
The heat exchange tube provides a way of incorporating in the accumulator a mechanism for heat exchange between the high pressure side of the system, i.e. between the outlet of the compressor, the condenser and the expander valve, and the low pressure side of the system. As such the tube can embody any of the enhancements known or obvious to those skilled in heatexchanger art, such as those designed to increase surface area. Further, although the preferred embodiment is a single, continuous tube other configurations are possible. Effective heat exchange is accomplished by circulating the relatively hot refrigerant from the high pressure side through the heat exchange tube while passing over this heat exchange tube the gaseous refrigerant leaving the accumulator and being delivered to the inlet of the compressor. This both pre-cools the liquid refrigerant prior to expansion, increasing the system cooling capacity, and helps to ensure that the refrigerant gas flow reaching the compressor does not contain any liquid refrigerant. The effective heat exchange is accomplished with minimal increase in suction line pressure loss and without compromising the accumulator function. The heat exchanger disclosed herein has few additional parts, is more effective, and in its preferred embodiments is easier and cheaper to manufacture than accumulator and internal heat exchanger combinations as known in the prior art.
Preferably the heat exchange tube is arranged in the form of a helical coil in the annular passage between the outer housing and the inner liner of the accumulator so as to define in that angular passage a helical flow path for the refrigerant vapor along the length of the coil. The outer diameter of the heat exchange tube is matched to the width of the annular passage between the outer housing and the inner liner and thus virtually all of the refrigerant gas flow travels the full length of the helical path.
The inner liner is preferably fabricated in a plastic material of poor heat conductivity so that the liquid refrigerant contained therein is insulated from the heat of the coil and of the outer housing.